This invention pertains to heat-responsive thermal elements usable for actuation of devices such as fluid control valves which are responsive to temperature of the fluid.
For many years, various types of control devices which are temperature-responsive have been operated by a thermal element. The thermal element has a casing carrying a charge or volume of material expandable in response to heating thereof with such material typically being a wax material. The thermal element also has motion-transmitting means for transmitting the force created by the heat-expandable wax to a member to be operated, such as the valve member of a fluid valve such as a relief valve and also structure to form an interface between the wax material and the motion-transmitting means. Such interfaces have typically utilized either O-rings or other forms of hollow cylindrical seals. Such prior devices have required some structural part to impart a radially outwardly force to form a seal with the casing of the thermal element.
Some of the prior art thermal elements have attempted to prevent flow of a part of the controlled fluid to a location between the motion-transmitting structure and the sealing structure which imposes additional design requirements for the thermal element.